A port scanner in Ocaml. Rudimentary form done to learn how Ocaml does networking.

jmap.ml

module Scanner = struct

  (* attempt to open a port and return an option *)
  let open_port host port timeout = fun () -> 
    let open Lwt.Infix in
    let sockaddr = Unix.ADDR_INET (Unix.inet_addr_of_string host, port) in
    let socket = Lwt_unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
    Lwt.catch
      (* Port is open *)
      (fun () ->
        Lwt_unix.connect socket sockaddr >>= fun () ->
        Lwt_unix.close socket >>= fun () ->
        Lwt.return (Some port) 
      )
      (* Port is closed *)
      (fun _ ->
        Lwt_unix.close socket >>= fun () ->
        Lwt.return None 
      )

  (* scans a port by trying to open it or timing out *)
  let scan_port host port timeout =
    let open Lwt.Infix in
    let connect_task = open_port host port timeout in
    let timeout_task = Lwt_unix.sleep timeout >>= fun () -> Lwt.fail Lwt_unix.Timeout in
    Lwt.pick [connect_task (); timeout_task] >>= function
    | Some port -> Lwt.return (Some port)
    | None -> Lwt.return None

  (* scans a range of port *)
  let scan_ports host start_port end_port timeout =
    let open Lwt.Infix in
    let ports = List.init (end_port - start_port + 1) (fun i -> start_port + i) in
    let scan_results =
      List.map (fun port ->
        scan_port host port timeout >>= function
        | Some port -> Printf.printf "Port %d is open\n" port; Lwt.return ()
        | None -> Printf.printf "Port %d is closed\n" port; Lwt.return ()
      ) ports
    in
    Lwt.join scan_results

end

let () =
  let host = "127.0.0.1" in
  let start_port = 8000 in
  let end_port = 8090 in
  let timeout = 2.0 in
  let open Lwt.Infix in
  Lwt_main.run (
    Scanner.scan_ports host start_port end_port timeout >>= fun () -> Lwt.return ()
  )